Field of the Invention
The present invention relates to a technique to reduce jaggies in an edge portion in image data.
Description of the Related Art
Conventionally, in an image forming apparatus, several techniques to reduce ruggedness called jaggies, which occurs in the edge portion of a character or the like, have been proposed. There are a variety of reasons for the occurrence of jaggies, but it can be thought that the main reason is ruggedness of pixels caused by a low-resolution printer and ruggedness accompanying screen processing.
As a technique to improve ruggedness accompanying screen processing, for example, there is a technique to generate corrected data from the image data before screen processing and to add the corrected data to the edge portion of the image data after the screen processing so that the edge portion is rimmed therewith (e.g., see Japanese Patent Laid-Open No. 2006-295877). In this technique, whether or not the edge portion is an edge portion on which edge correction processing should be performed is determined and in the case where the edge portion is an edge portion that needs edge correction processing, the corrected data and image data after the screen processing are compared, and then the data whose value is greater is output, and thereby, jaggies caused by the screen processing are reduced. Further, with this technique, the ruggedness of pixels caused by a low-resolution printer, which is described earlier, is also reduced at the same time even though the configuration is simple.
The method of Japanese Patent Laid-Open No. 2006-295877 is a method in which the corrected data consisting mainly of half dots and the image data after the screen processing consisting mainly of full dots are combined and then output to the edge portion. Because of this, the edge portion consists of different dots, i.e., half dots and full dots, and there is a case where a half dot is absorbed by a nearby full dot, and therefore, the degree in reduction in jaggies in the edge portion is small. The reason is that toner is pulled to a deeper position of a latent image in the position where a shallow latent image of the corrected data neighbors a deep latent image of the image data after the screen processing at the time of development in the case of the electrophotographic scheme. As a result of this, development is hard to progress in the shallow latent image portion, and therefore, there is a case where the degree in reduction in jaggies in the edge portion is small.